How to warm up a domain for cold email

What warm-up is, and what it is not

Warm-up means sending a small amount of real, wanted mail from a new mailbox, increasing slowly, so that providers see consistent, ordinary behavior. Google's own guidance for senders says to increase volume gradually and to cut back if mail starts to bounce or be deferred.

Warm-up does not fix broken DNS, does not remove a blocklist listing and does not rescue a bad list. If authentication is wrong or you send to people who do not want your email, no amount of warm-up will help.

Step 1: set up authentication before sending anything

Before the first message, publish SPF, set up DKIM signing for your own domain and publish a DMARC record. Then verify them. See the DMARC guide and the DKIM guide for Google Workspace. Our free checker will confirm all of it in a few seconds.

Step 2: use a domain and mailboxes that make sense

Use a separate domain for outreach rather than your main company domain, so any reputation damage stays contained. See using a secondary domain for cold email. Spread volume across several mailboxes instead of pushing one mailbox hard. Give each mailbox a real name and a short, ordinary signature.

Step 3: start small and steady

In the first week, send only a handful of messages per mailbox per day, to people who are likely to open and reply, such as colleagues, friends and existing contacts who agree to help. The aim is real two-way conversation, not volume. Then raise the daily number in small steps. Predictability matters more than speed: a steady line looks normal, while spikes look suspicious.

An example ramp

This is an illustrative pace, not an official one. Adjust it down if anything looks wrong.

• Weeks 1 to 2: roughly 5 to 15 messages per mailbox per day, mostly to known, friendly contacts.
• Weeks 3 to 4: increase gradually, and begin including a small share of real prospects.
• Weeks 5 and beyond: scale up in small increments only if bounces and complaints remain low, and stop increasing when you reach the per-mailbox volume your sending tool and provider recommend.

Many experienced senders keep cold volume per mailbox modest even after warm-up, and add mailboxes rather than pushing each one harder.

What to watch while you warm up

• Bounce rate: rising bounces mean list problems or reputation trouble.
• Spam complaints: set up Google Postmaster Tools for the domain, so you can see Gmail's reported spam rate once you have enough volume.
• Replies: real replies are the strongest positive signal.
• Placement tests: periodically send a test to your own Gmail, Outlook and Yahoo accounts and check where it lands.
• Blocklists: check weekly. See how to check whether your domain is blacklisted.

A word on warm-up tools

Automated warm-up networks send mail between participating mailboxes to simulate engagement. Some people find them useful, but providers have never confirmed that they work, and artificial engagement is not the same as real recipients wanting your mail. If you use one, treat it as a supplement to careful volume control and a clean list, not a replacement for either.

When to slow down or stop

Pause increases, or reduce volume, if you see a jump in bounces, deferrals such as 4xx temporary errors, a message landing in spam in your tests, or a blocklist listing. Find the cause before ramping again. Sending harder into a problem tends to make it worse.

Keep monitoring after warm-up

Warm-up ends, but reputation does not stay fixed. DNS can be changed by mistake, a listing can appear overnight, and an old tool can break your SPF. That is the reason to keep checking your domain regularly. OutboxWatch does this automatically with daily checks and alerts, and the free checker is there for one-off tests.